US President Barack Obama's state visit to Vietnam starts Monday. US-Vietnam ties have attracted great attention for being one of the sensitive, uncertain factors in the South China Sea, and opinions differ on how far the relationship can go.

The tour is overdue. Last year marked the 40th anniversary of the end of the Vietnam War, as well as the 20th anniversary of the normalization of US-Vietnam diplomatic relations, but Obama has not visited the nation until now. It means that Hanoi is not the most important partner for Washington and things related to Hanoi can wait. However, the visit also reflects that this bilateral relation is significant enough that Obama has to come once before stepping down.

It is predicted that the Trans-Pacific Partnership (TPP) and the South China Sea will be on the agenda of talks between the two sides. Hanoi is hoping that the US will completely lift restrictions on arms sales to Vietnam, which obviously cannot be achieved. The US public opinion field is expecting Obama to raise the topic of human rights.

The South China Sea issue is drawing the US and Vietnam closer. Yet the different ideology is constantly pushing them away. Hanoi wants to gain more leverage from the US to contain China in the South China Sea, making it a bargaining chip in its territorial disputes with Beijing. Meanwhile, it also hopes to develop its own economy by strengthening ties with the US. To Washington, if Hanoi could get closer to Washington like the Philippines and Singapore - providing military bases to the US - the White House' rebalance to the Asia-Pacific region will gather new momentum. Nevertheless, it is impossible that both sides can overcome their concerns over each other. US society is severely biased toward the regime helmed by the Communist Party of Vietnam (CPV). During the latter stage of the Vietnam War, a large number of Vietnamese fled to the US. Those people are more interested in overturning the current Vietnamese regime than in the South China Sea.

But Vietnam won't become another US ally like the Philippines. It has always been worrying over its gains and losses in its ties with the White House. In the meantime, although Beijing is a major opponent of Hanoi over territorial disputes in the South China Sea, the former is also considered by Hanoi's mainstream elites as a political pillar for Vietnam's stability. The legitimacy of the CPV's rule mainly comes from the long-term stability and prosperity of China, a socialist country.

Vietnam will attach equal importance to its ties with both Beijing and Washington. It hopes to maximize its own interests, but Hanoi is also well aware that it has to be very scrupulous.